2.4 Transition Metals
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Define a transition metal
An element which forms at least one stable ion with an incomplete d subshell.
Where are transition metals located in the periodic table ?
In the d subshell (between g2 and g3)
What are some physical characteristics of transition metals ?
• Good conductors of heat and electricity • High mp and bp • Shiny • Low reactivity
What are the characteristic chemical properties of transition metals ?
• Variable oxidation states • Form coloured compounds in solutions • Good catalysts • Form complex ions.
Define the term ‘complex ion’
A transition metal is central in a molecule surrounded by ligands (other molecules/ions) that are co-ordinate bonded to it.
Give three examples of transition metals catalysts and the reactions
Iron - Haber process Vanadium oxide (V2O5) - Contact process MnO2 - Decomposition of H2O2.
From what subshell do transition metals lose electrons first from when forming ions ?
4s.
Define the term ligand
• An ion or molecule with at least one lone pair of electrons • Donates them to a transition metal to form a co-ordinate bond and thus a complex ion.
Define the term mono/unidentate ligand
A ligand that forms one co-ordinate bond to the central transition metal in a complex (one lone pair to donate).
Define the term bidentate ligand
A ligand that forms two co-ordinate bonds with a central transition metal in a complex ion (two lone pairs to donate).
Define the term multidentate ligand
A ligand that forms three or more co-ordinate bonds with a central TM ion in a complex ion.
Give some examples of common monodentate ligands
• Cl- • H2O • NH3 • CN-
What is the formula for an ethanedioate ion ? How many co-ordinate bonds can it form in a complex ?
• C2O4 2- • Forms two co-ordinate bonds, bidentate
—
—
How many co-ordinate does ETDA 4+ form ?
6.
Define the term co-ordination number
The number of co-ordinate bonds a transition metal has made with surrounding ligands in a complex ion.
What is the Chelate effect ?
Chelate complexes with multidentate ligands are favoured over monodentate ligands or ligands that form fewer co-ordinate bonds per molecule.
Explain the chelate effect in terms of entropy and the reaction that is occurring
• The number of molecules increases when multidentate ligands displace ligands that form fewer co-ordinate bonds per molecule • This gives a significant increase in entropy • The Gibbs free energy change is <0 which makes it a feasible reaction • Therefore a more stable complex ion is formed.
What ion is typically formed when a transition metal dissolves in water ?
• An aqua ion • 6 H2O ligands form around the central ion • Octahedral complex ion shape.
If a transition metal has two ligands in a complex ion what is it’s shape ?
Linear.
If a transition metal has 4 ligands in a complex ion what is its shape ?
Tetrahedral
Name an exception to the rule that a complex ion with 4 ligands has a tetrahedral shape
Platin (platinum 2+) forms square planar molecules.
What shape is a complex ion if it has 6 ligands ?
Octahedral
How can complex ions display cis-trans isomerism ? What shapes of ions does this apply to ?
• Ligands can differ in the way they are arranged in space • When two of the same ligand are on opposing sides of the central ion the complex is a cis isomer • When two of the same ligand are on the same side of the central ion the complex is a trans isomer • This applies to square planar and octahedral complex ions.